If you are using all wireless, you can use a 0 port router as long as it has wireless on it. Why do you need a switch for wireless?
The issue would be that you will probably need several WiFi access points though-out the building, which means you'll need a wired connection to those access points. But a router with 16 ports should be plenty, you'll need a access point every few rooms probably. If you have more than 30 rooms, you'll need a larger switch.